888 research outputs found

    The practical application of an enhanced conveyance calculation in flood prediction

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    An enhanced one-dimensional mathematical model for simulating flood levels and calculating stage-discharge relationships is presented. Enhanced conveyance subroutines have been developed and incorporated into the commercially available river modelling software ISIS. The newly developed software has been verified using experimental and field data. When a river overtops its banks there is a vigorous interaction between slow moving flood plain flow and faster moving main channel flow. This interaction mechanism has been the focus of intense research over the past forty years. A selective review of this research is detailed with particular attention to the case of meandering channels. The Ackers Method and the James and Wark Method are two discharge capacity methods that have emanated from this recent research and are considered to be the most practically suitable methods and are indeed recommended by the Environment Agency of England and Wales. The methods account for interaction effects when flow is overbank in a straight and meandering channel respectively. It is these methods that have been incorporated into the commercially available and industry leading one-dimensional river model ISIS to enable an enhanced conveyance calculation. The newly developed software has been tested against the Flood Channel Facility Series A and B experiments to a satisfactory level of accuracy. The testing included predicted of stage discharge relationships and water level prediction. In addition it has been applied to the River Dane in Cheshire which is highly meandering and suited to the James and Wark methodology. This was intended to give practical advice concerning the use of the James and Wark Method and the degree of accuracy in estimating the 'channel parameters' which are required by this method. The results of this work showed that a significant rise in water level prediction is obtained when using the enhanced code. Also, it was clear that a high degree of accuracy was not required in estimating the 'channel parameters' with the possible exception of the sinuosity term

    Studies in Natural Products: Sesquiterpenoids of Brachylaena hutchinsii

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    The chemical constituents of Brachylaena hutchinsii, a hardwood indigenous to East Africa, have been examined, and sesquiterpenoids of the heartwood extract and of the steam-volatile oil (Essential Oil Muhuhu) have been investigated. The first part of the thesis is concerned with the chemical composition of the heartwood and, in particular, with the structures of the Brachylaenalones, principal sesquiterpenoid constituents of an extract of the heartwood. In the present work, structures (A), proposed earlier, for these compounds, are re-examined and revised to structures (B) in the light of further evidence. In addition, the products of hydride reduction of the Brachylaenalones, previously reported to be three diastereomeric diols, are re-investigated and, in consequence of a refinement in analytical procedure, the occurrence of the fourth, expected diol is established. This work has necessitated the use of a wide range of analytical techniques, and physico-chemical data of the Brachylaenalones, the diols and the corresponding ketols have been recorded and analysed. Chemical correlation of the Brachylaenalones with the expected parent hydrocarbons, copaene and ylangene, has been attempted by several routes, but the desired transformations have been accompanied by side reactions, leading to complex mixtures of products in each case. Reduction of the dithioketal derivative of one ketoaldehyde over Raney nickel catalyst yielded a mixture of products comprising neither copaene nor ylangene: reduction of each ketoaldehyde according to the Wolff-Kishner method, however, afforded the parent hydrocarbons as minor products. In the second part of the thesis, a survey of the chemical constituents of the steam-volatile oil from the heartwood is described, and comparisons are drawn with the composition of the heartwood extract. Separations of the oil into fractions by gas-liquid chromatography (analytical and preparative), together with combined gas chromato-graphic-mass spectrometric analyses of individual fractions, supplemented in some instances by infra-red spectrometry, has allowed the documentation of molecular weights and functional types present in the oil, and the tentative identifications of copaene (C), ylangene (D) and ylangenol (E). The Brachylaenalones were not present in the oil, which comprised mainly compounds of molecular weights in the range 200-222

    Ageing, telomeres, senescence, and liver injury

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    Populations in developed countries continue to grow older and an understanding of the ageing process to allow healthy ageing carries important medical implications. Older individuals are more susceptible to most acquired liver disorders and more vulnerable to the consequences of liver disease. Accordingly, age is a critical determinant of outcome for hepatitis C virus infection and liver transplantation. In this review we describe changes in the ageing liver and discuss mechanisms of senescence at the cellular level. In particular, we focus on mechanisms by which inflammation, oxidative stress, and oncogenic stress accelerate cellular senescence. In the setting of chronic hepatic injury and inflammation, cellular senescence functions as an essential stress-response mechanism to limit the proliferation of damaged cells and reduce the risk of malignancy, but this benefit is achieved at the expense of senescence-related organ dysfunction. The dual role of cell senescence in chronic liver disease will make this an intriguing but challenging area for future clinical interventions